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May 8, 2020 1:38 AM
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Can anyone tell me what is the _Std Dev value in the table that is created using the command Save Limits in New Table of control chart platform? I suppose it is the standard deviation of the dataset, but the value I see is different from the value that is calculated, for example, using the Table Summary Std Dev. I verified that using different datasets, JMP 15.1, JMP13. Is there anything that i misunderstand?

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The _StdDev value is the mean of each of the subgroup's standard deviations.

Jim

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The _StdDev value is the mean of each of the subgroup's standard deviations.

Jim

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Re: question about _Std Dev on limits table created by control chart platform

Make sense! Thanks a lot!

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Re: question about _Std Dev on limits table created by control chart platform

Your question is about the **most basic aspect** of a control chart: the estimation of the short-term process variability in the absence of a special cause (in control state). Your question suggests that you have not learned about the purpose and construction of a control chart. While the control chart is 'just' a run chart with limits representing the natural variation, its simplicity does not mean that 'just' anyone can use it properly. I recommend that you start learning by reading the relevant chapters from **Help > JMP Documentation Library > Quality and Process** guide. Then seek one of the books by **Doug Montgomery** or **Don Wheeler**, to name a couple of experts.

If you are charting important data to make important decisions then learning about proper control chart analysis is worth your time.

Learn it once, use it forever!

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